The invention relates to steerable nozzles for rocket engines.
The field of application of the invention is more particularly but not exclusively that of missiles, in particular tactical missiles having a diameter of less than about 500 millimeters (mm).
A steerable-nozzle rocket engine comprises a casing defining a combustion chamber that opens out through a rear end wall, at least one nozzle comprising a moving diverging portion and a static portion, a jointed link device connecting the moving diverging portion and the static portion, and an actuator device acting on the nozzle to change its orientation, and consequently to change the direction of the thrust vector produced by combustion gas being ejected from the chamber.
A known jointed link device uses a laminated spherical abutment made up of a stack of metal or composite material layers alternating with layers of resilient material bonded to one another. Such a device enables the nozzle to swivel to a limited extent relative to the casing by deformation of the resilient layers in shear. The laminated abutment is mounted so that it is normally stressed in compression under the effect of the force exerted by the combustion gas on the nozzle, given its limited strength against tension forces. Unfortunately, in certain configurations, the laminated abutment can be subjected to tension forces. In addition, laminated abutments are sensitive to aging and it is difficult to make laminated abutments that are capable of withstanding a very wide range of temperatures.
In order to overcome the above drawbacks, proposals have been made for a nozzle with a steerable diverging portion that presents a spherical surface in direct contact with a complementary spherical surface formed on the static portion of the nozzle (ball and socket system), a change in the orientation of the diverging portion of the nozzle being accompanied by the spherical surfaces sliding one over the other. The portions of the moving diverging portion and of the static portion of the nozzle that are in mutual contact are typically made of a carbon/carbon (C/C) composite material which presents good thermo-mechanical behavior, in particular at high temperature, and high resistance to ablation. Such a mount avoids the drawbacks of mounts having laminated spherical abutments, but the problem to be solved is that of providing gas-tightness between the contacting spherical surfaces for all orientations of the diverging portion of the nozzle. To achieve this, it is necessary to provide permanent contact between the ball and the socket regardless of the angle of activation. Preliminary tests have been performed with such a steerable nozzle. Those tests have shown that the concept is viable but with limitations on control in the pitch and yaw planes, with the ball being pressed against the socket by prestressed actuators.